This invention relates to a bipolar signal generating apparatus having an ability of delivering a bipolar digital signal having positive and negative polarities to a transmission line.
A conventional signal generating apparatus adapted to gransfer a bipolar digital signal, which has widely been utilized in data transmission fields, to a transmission line is most generally composed of a converter circuit adapted to be supplied with two kinds of signals and a transformer having a primary winding connected to output terminals of the converter circuit and a secondary winding connected across a pair of lines for constituting a data transmission line, so-called data path. This converter circuit functions, when a first input signal has an "H" level, to cause a current to flow in one direction through the primary winding of the transformer and, when a second input signal has an "H" level, to cause a current to flow in a reverse direction through the primary winding of the transformer. As a result, in the secondary winding of the transformer is generated a bipolar signal having positive and negative levels. When both the two input signals have "L" levels, respectively, the primary winding is cut out of both an electric source and ground, so that an output level of the secondary winding is located at a neutral region. Since the primary winding of the transformer has a high impedance when it is cut out of both the electric source and ground, the output signal delivered from the secondary winding of the transformer has not a correct rectangular wave form.